From what I gathered, the bug happens when GCVideo converts from the GC’s native signal format of YCbCr to RGB. Component video output was unaffected. Extrems demonstrated this via screenshots on his page: https://www.gc-forever.com/wiki/index.php?title=Game_Boy_Interface/High-Fidelity_Edition#Video_quality
Unfortunately, not all GCVideo solutions are easily upgradable; Some of the plug-and-play versions would first require cutting open, then adding a connector for a firmware programmer. If you have an upgradable board and a programmer, it seems like an easy an essential fix and Dan will be making a how to update guide for current GCDual users.
Here’s a diagram created by Chriz2600 that’s a clear visualization of the issue (click for full-sized):